The present invention relates to an optical waveguide sheet which is utilized for reading facsimile image information.
Conventionally, reading of facsimile image information is carried out using an optical sheet in which a plurality of optical fibers having a photo-absorption layer are arranged in a flat plate-like form, or using an optical waveguide sheet in which a scatterer portion having a low reflection factor is formed. The latter is made of a transparent plastic sheet impregnated with a polymeric monomer, on which light or an electron beam is irradiated while polymeric conditions are controlled and proper heat-treatment is carried out.
FIGS. 14-16 show conventional examples of optical waveguide sheets used for reading of image information.
FIG. 14 depicts a first example of an optical sheet 41 in which optical fibers 44 composed of a core portion 42 and a cladding portion 43 are arranged in parallel and a plurality of photo-absorption layers 45 are formed in the voids at the outer circumference of the fibers 44. FIG. 15 depicts a second conventional example of an optical waveguide sheet, in which a polymeric monomer is reacted and polymerized with transparent plastic. This portion 47 has a low reflection factor, and functions as a cladding layer since light scatterers are formed inside the portion by the controlled polymeric conditions and heat-treatment. Reference numeral 48 denotes a core portion in which a reflection factor of the transparent plastic composing a base does not change even from the application with the above treatment. FIG. 16 is a section view along a direction A shown in FIG. 15 in which reference numeral 49 denotes scatterers, reference numeral 50 denotes incident light entering at an angle which is greater than a critical angle determined by the respective reflection factors of a core portion 51 and a cladding layer 52, reference numeral 50a denotes a path of incident light in the case of an absence of scatterers 49, reference numeral 53 denotes incident light entering at an angle which is smaller than the critical angle, reference numeral 54 denotes a copy surface, reference numeral 55 denotes a photo-sensor surface, and reference numeral 56 denotes scattered light. From among the light reflected from the illuminated copy surface, the incident light entering at an angle which is smaller than the critical angle is repeatedly totally-reflected at the boundary of the cladding layer 52 to reach the photo-sensor surface 55. However, if a scatterer exists on the boundary portion upon such reflection, the reflection efficiency is reduced due to light scattering. Additionally, the incident light entering at an angle which is greater than the critical angle is scattered due to the presence of the scatterers 49 in the cladding layer 52, and only a small amount of light enters the adjacent core portion 51a.
In the first conventional example, proper arrangement of the optical fibers is extremely difficult, and hence it is too costly to achieve. In the second conventional example, the manufacturing cost is relatively low, but since the incident light is reflected by the scatterers, light denoting read image information on the copy surface is not totally reflected, thus reducing the transmission efficiency of light arriving at the photo-sensor surface 55.